This invention relates to a method for separating hydrocarbons from drill cuttings produced during drilling operations.
For drilling of oil and/or gas wells, a drill bit at the end of a drill string produces rock cuttings as it cuts through subsurface rock. Drilling mud circulated from the surface to the drill bit and back to the surface carries these cuttings to the surface. These cuttings are often contaminated with hydrocarbons either from the formations being cut by the drill bit, or by fluids in the drilling mud. At the surface, the drilling mud and cuttings are treated to separate the cuttings from the mud with mechanical treatment, for example by use of shale shakers, desanders, desilters, hydrocyclones and centrifuges. Drilling muds may be water based, oil based and may be mixtures of the two (emulsions). Invert drilling muds are in common use where the oil is the continuous phase, and water or brine is emulsified within the oil as the dispersed phase. Removing hydrocarbons from drilling cuttings carried by invert drilling muds is a particularly difficult task. A mixture of drill cuttings and invert drilling mud will be referred to as invert mud drill cuttings.
U.S. Pat. No. 6,838,485, discloses a method that moves away from mechanical treatment of the drill cuttings and uses a chemical treatment to separate hydrocarbons from drill cuttings carried by an invert drilling mud. In this patent, it is stated that “drilled cuttings may be treated using any suitable system of equipment. After separation from the drilling mud, the contaminated cuttings typically pass through a holding bin into an inlet hopper. The cuttings preferably are treated directly in a batch mixer equipped with an appropriate inlet for the relevant solutions and an apparatus for low shear mixing, such as a paddle mixer. In a preferred embodiment, the cuttings are sprayed with an emulsifying solution effective to transform the free hydrocarbons in the cuttings into an emulsion. The emulsion thereafter is treated with an encapsulating material to encapsulate the emulsified hydrocarbons, and the mixture of drill cuttings and encapsulated free hydrocarbons is released into marine waters where it disperses.” The emulsifiers are specified to be a combination of non-ionic emulsifiers with anionic emulsifiers.
The invention described here is intended to provide enhanced recovery of hydrocarbons from invert drill cuttings by mechanical action, without the necessity of using emulsifiers.